What does reinstalling macOS actually do?
Reinstalling macOS erases the startup disk and installs a fresh copy of the operating system (macOS). It does not erase other disks or partitions on your Mac – only the disk that macOS is installed on will be affected (1). User files and data that are stored on external drives or in cloud storage will not be erased or changed in the process. Reinstalling macOS essentially resets your Mac’s primary hard drive while leaving user data intact.
When you reinstall macOS, it replaces system files, apps from Apple, and settings and preferences with the original defaults. This can fix software issues, system corruption, and performance problems caused by aging system files. However, your personal data, such as documents, photos, music, and downloaded apps, remain untouched as long as they are stored outside of the macOS startup disk. Reinstalling is a way to get a “clean slate” for the Mac operating system without deleting your files (2).
Will reinstalling delete my files and data?
When you reinstall macOS, all files and data on the startup disk itself will be deleted. This is because the process completely erases the existing macOS installation and installs a fresh copy. However, your files on external drives or cloud storage will remain intact during the reinstall.
Specifically, reinstalling macOS deletes everything on the startup drive except for a few user settings and configuration files. This includes your user accounts, applications, documents, photos, music, settings, and any other personal data stored locally on the startup disk. The macOS installer essentially resets the startup disk to its factory settings.
In contrast, any external drives plugged in or cloud services connected to your Mac will be unaffected. So files stored on a USB drive, SD card, external hard drive, Time Machine backup, iCloud Drive, Dropbox, OneDrive, etc. will not be erased or altered by reinstalling macOS. The startup disk is the only location wiped clean.
As noted on Apple’s forum, you can safely reinstall macOS without worrying about losing data stored separately from the startup disk. Just be sure to have backups before proceeding.
How to backup your data before reinstalling
Before reinstalling macOS, it’s crucial to backup your important files and data so you don’t lose anything in the process. There are a few key ways to backup your Mac:
Use Time Machine: Time Machine is Apple’s built-in backup solution that creates incremental backups of your Mac to an external drive like a USB or Thunderbolt drive. To set it up, go to System Preferences > Time Machine and select a drive to use for backups. Time Machine will automatically backup hourly snapshots of your files so you can restore to any point in time.
Clone your startup disk: You can create a bootable clone of your entire startup drive using a tool like Carbon Copy Cloner or Super Duper. This replicates everything including your operating system, apps, files and settings. You can boot directly from the clone drive if needed. See Apple’s instructions on cloning your startup disk.
Manual file copy: At a minimum, you’ll want to manually copy your important documents, photos, music and other files to an external hard drive or cloud storage like iCloud or Dropbox before reinstalling. This preserves your critical user data.
Backing up properly ensures you won’t lose your files and gives you options to restore your apps, settings and system at any time. See Apple’s guide on backing up your Mac for more tips.
How to reinstall macOS
There are a couple ways to reinstall macOS on your Mac computer. The easiest is to boot into Recovery Mode and reinstall from there.
To boot into Recovery Mode, restart your Mac and hold down Command + R as it restarts. This will boot you into the Recovery environment. From here, you can select Reinstall macOS from the Utilities window and follow the prompts to reinstall the operating system.
You’ll have the option to keep your files and data or erase your drive and start fresh. Selecting keep your files will reinstall macOS but maintain your user accounts, documents, photos, etc. Choosing erase will completely wipe your drive before reinstalling.
You can also reinstall macOS using the macOS installer from the App Store. Download the version of macOS your Mac originally had and run the installer. Again, you’ll have options to keep data or erase the drive (source).
Reinstalling macOS is a handy trick to fix many common issues and refresh your Mac. As long as you backup important data first, it is generally a safe process.
Reasons to Reinstall macOS
There are a few key reasons you may want to reinstall macOS on your Mac:
Fix software issues, crashes, or bugs – Over time, bugs, crashes, and other errors can accumulate in your operating system files, applications, and preferences. Reinstalling macOS essentially resets these system files and settings, which can help resolve persistent software issues and instability.
Improve performance – A fresh install of macOS can help speed up a Mac that has become sluggish over time. The reinstall clears out clutter, removes old and unused files, and resets your system preferences to defaults, allowing your Mac to run faster and smoother.
Remove clutter and bloat – As you use your Mac over months and years, cruft builds up from various apps, files, downloads, caches, logs, and more. A reinstall wipes the slate clean, removing unneeded files that are simply taking up space and slowing things down.
Potential downsides of reinstalling
While reinstalling macOS can often fix issues and improve performance, there are some potential downsides to be aware of:
The biggest risk is accidental data loss if you don’t properly back up your files first. The reinstall process itself does not delete your data, but any mistakes during the process could result in data being erased (1). So it’s essential to create a full backup of your drive before reinstalling.
You will also have to reinstall any software you were using after the OS reinstall. This can be time-consuming, as you’ll have to find installers, license keys, and redo preferences for each application. User settings and configurations will also be reset back to defaults (2).
Finally, while rare, some users report issues like hanging, crashes, or slower performance after reinstalling. So reinstalling does not guarantee improved system performance.
Overall, as long as you properly back up your data first, the benefits of a fresh OS install often outweigh the time investment to reconfigure software. But it’s helpful to be aware of the potential downsides before deciding to reinstall macOS.
When should you reinstall vs. other options?
Reinstalling the operating system can fix issues caused by damaged system files or settings. According to Apple Support, if your Mac is experiencing crashes, slowdowns, or other issues that persist after restarting, reinstalling macOS may help resolve the problem. However, reinstalling should not be the first solution you try.
If your Mac feels sluggish or applications are not performing well, try using built-in tools like Disk Utility and OnyX first to clean up the disk and optimize system performance. You can also reset NVRAM and SMC to troubleshoot certain issues before considering a reinstall.
In some cases, minor bugs or app compatibility problems that develop after an OS update can be fixed by reinstalling the OS without erasing your data. Try using the “Reinstall macOS” option in Recovery first before wiping your drive.
Only when you have an issue that persists across basic troubleshooting should you consider fully erasing your disk and reinstalling macOS. This is best saved as a last resort since it will delete all your data.
Reinstalling and user accounts
When reinstalling macOS, you have the option to keep your existing user accounts and settings or erase everything and start fresh. According to Apple Discussions, after a successful reinstallation of macOS, any user accounts that existed previously will still be available to log into after the reinstall. Reinstalling will not delete or reset your user accounts by default.
However, you also have the option to erase your entire hard drive when reinstalling macOS. This will delete all user accounts and reset the Mac as if it was brand new. As noted on Reddit, if you choose to erase your hard drive, all user accounts will be removed. You’ll have to create new accounts and reset passwords after the reinstall completes.
So in summary, reinstalling macOS itself does not delete or reset user accounts, but you can choose to erase everything if you want to start fresh with no existing accounts or settings.
Reinstalling and Resetting Passwords
One benefit of reinstalling macOS is that it gives you the option to reset a forgotten account password. If you forgot your login password, reinstalling the OS will allow you to reset it without needing your current password.
When you reinstall macOS and reach the setup screen, you’ll have the option to enable “Reset Password” under Setup Assistant. This will let you reset the passwords for all accounts on that Mac. According to Apple Support, this option is only available right after reinstalling the OS [1].
Reinstalling the OS essentially resets all settings, so it wipes out your current password and lets you create a new one from scratch. This can be useful if you forgot your login password and none of the usual password reset options are working.
However, reinstalling just to reset a password should be a last resort. You’ll lose all your apps and settings in the process. First try resetting your password using Apple’s instructions, like using Password Assistant from Recovery Mode [2] or the “Restart password options” from the login screen [3].
FAQs and Common Mistakes When Reinstalling macOS
Many users have questions or run into issues when reinstalling macOS. Here are some of the most frequently asked questions and common mistakes to be aware of:
One source of confusion is exactly what data gets deleted when reinstalling macOS. As per Apple Support, reinstalling the OS does not delete your files, photos, music, movies, apps, or other user data. Your data should remain intact after reinstalling. However, it’s always wise to back up your data beforehand just to be safe.
That leads to the second common mistake – forgetting to properly back up your data first. As users on Apple Discussions have noted, you’ll want to create a full backup of your entire system using Time Machine before starting a reinstall. This will save you from any potential data loss.
Finally, some users encounter issues reactivating software after reinstalling macOS. Most apps will automatically relink to your user account and reactivate after reinstalling the OS. But occasionally you may need to manually reactivate apps using your license key or account login. Checking with the app vendor beforehand can avoid any post-reinstall activation problems.
Following proper backup procedures and understanding what data is impacted by a reinstall can help avoid these common FAQs and mistakes.